3800 holy shit i have a problem
- Thread starter Sinister Drag Designs
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the temperature readings you are seeing are not from the pcm its from the input from the IAT sensor or now your timing commander.
The way this trick works is that there is a table that is modified in the pcm air temp vs cylinder pressure vs timing. For a given air temp, we can tweak timing.
So what we do is we make it so that at select temperatures we tell the pcm to overall add or subtract timing.
the timing commander or the happy knob or the slp timing module or the 1.99 10K potentiometer from rat shack all work by lying to the pcm about the temperature.
The iat sensor is nothing more than a temperature sensitive resistor. If you know the proper resistance values, you can "fool" the pcm into seeing whatever temperature you like and that in turn triggers the timing adjustment.
The pcm/scantool will report whatever temperature it sees based on the resistance of the IAT circuit. If its reporting a weird value, you'll want to check how you have that circuit connected as something isn't wrong there. This WILL affect the timing as whatever temp you are seeing, it will try to match that up to the timing table (if its within -40 to +80 C). You CANNOT go colder than -40 but you MIGHT be able to get the pcm to report a higher value than 80C .... If the value the pcm sees is outside of the this window, its probably going ot ignore the data.
However, you need to be careful if you have timing tables in the pcm and you have something driving the IAT that is not working correctly... Imagine the following scenario.
PCM
-----
0 C (32F) = +6 degrees
10 C = +4 deg
20 C = +2 deg
30 C = +0 deg
40 C = -2 deg
50 C = -4 deg
60 C = -6 deg
Now, the way it should work is you hook up your timing contro ldevice and you "dial in" +4. What this actually does is set the resistance necessary to make the pcm see ... 10 C
*IF* you have a malfunctioning device or you have the normal IAT hooked up, if it hits a valid temp, you're going to get the timing associated with it. For instance, say your device sets it to 0C all the time... Guess what, you're going ot get +6 timing ALL THE TIME. This is not a good scenario.
The best thing to do until you can figure out the issue with the temp readings is to just disconnect the IAT. This will default it to -40 (or real close). The standard timing table makes no changes at that temp so it would be "safe"... You will most likely get your SES illuminated, but it will clear once the circuit is reconnected.
HTH
The way this trick works is that there is a table that is modified in the pcm air temp vs cylinder pressure vs timing. For a given air temp, we can tweak timing.
So what we do is we make it so that at select temperatures we tell the pcm to overall add or subtract timing.
the timing commander or the happy knob or the slp timing module or the 1.99 10K potentiometer from rat shack all work by lying to the pcm about the temperature.
The iat sensor is nothing more than a temperature sensitive resistor. If you know the proper resistance values, you can "fool" the pcm into seeing whatever temperature you like and that in turn triggers the timing adjustment.
The pcm/scantool will report whatever temperature it sees based on the resistance of the IAT circuit. If its reporting a weird value, you'll want to check how you have that circuit connected as something isn't wrong there. This WILL affect the timing as whatever temp you are seeing, it will try to match that up to the timing table (if its within -40 to +80 C). You CANNOT go colder than -40 but you MIGHT be able to get the pcm to report a higher value than 80C .... If the value the pcm sees is outside of the this window, its probably going ot ignore the data.
However, you need to be careful if you have timing tables in the pcm and you have something driving the IAT that is not working correctly... Imagine the following scenario.
PCM
-----
0 C (32F) = +6 degrees
10 C = +4 deg
20 C = +2 deg
30 C = +0 deg
40 C = -2 deg
50 C = -4 deg
60 C = -6 deg
Now, the way it should work is you hook up your timing contro ldevice and you "dial in" +4. What this actually does is set the resistance necessary to make the pcm see ... 10 C
*IF* you have a malfunctioning device or you have the normal IAT hooked up, if it hits a valid temp, you're going to get the timing associated with it. For instance, say your device sets it to 0C all the time... Guess what, you're going ot get +6 timing ALL THE TIME. This is not a good scenario.
The best thing to do until you can figure out the issue with the temp readings is to just disconnect the IAT. This will default it to -40 (or real close). The standard timing table makes no changes at that temp so it would be "safe"... You will most likely get your SES illuminated, but it will clear once the circuit is reconnected.
HTH
Email me and we can get it tested to see if it is the timing commander at fault. You haveto make sure that the positive and ground are good and clean. The only reason the timing commander would stick at a value is if it is not a good, clean postiive and ground. So far, I have heard of only one problem with the timing commanders out there (that was ron's) and it turned out to be a wiring problem. Let me know and we can work through it.
EDIT: Make sure the connection at the IAT is connected well also. Thinking back, I believe that was Ron's problem.
I
imported_Ron Vogel
Guest
My problem was my own fault. I had to splice in the IAT because my connector was long gone. During my header install, I pulled the motor forward and damaged one of the wires. I also used a "suspect" power source; which I have since fixed. The unit works fine for me now.
If the IAT wires are switched, or one of the leads gets grounded, I saw a floating resistance, and a corresponding floating temperature reading. I'm leaning toward Bob's problem being the power source to the unit.
did you read a word i typed ?
IAT tables being stock, modified, or otherwise would not cause you to have weird temperature readings...
275 F = 120C. ZERO, nada, zilch, zero, zip, timing adjustment would occur with a standard timing table if the IAT is reading 275degrees....... Now if you leave IAT connected and you're seeing ambient around 51 F that would come out to ... . -4 C and that would equate to about +1 degree of advance ....... Either scenario isn't going to allow you to see a change in timing (that is noticeable).
Go to radioshack and ask for a 10K linear potentiometer. They are $1.79. Get a scantool and monitor IAT temp. Dial it to +60C. Then go drive the car wot and monitor timing. You should be down quite a bit of timing. Lower the temp and at WOT you will see the timing increase.
NOTE : The timing table is not adjusted at idle so checking idle spark advance will not be helpful you will need to verify timing while at WOT.
NOTE 2 : You need to monitor KR and Timing at WOT. If you have knock, you will not be able to get more timing even if the knob is set to allow for more timing; however, yo ushould have more KR than you would with the knob with the timing adjusted downward....
IAT tables being stock, modified, or otherwise would not cause you to have weird temperature readings...
275 F = 120C. ZERO, nada, zilch, zero, zip, timing adjustment would occur with a standard timing table if the IAT is reading 275degrees....... Now if you leave IAT connected and you're seeing ambient around 51 F that would come out to ... . -4 C and that would equate to about +1 degree of advance ....... Either scenario isn't going to allow you to see a change in timing (that is noticeable).
Go to radioshack and ask for a 10K linear potentiometer. They are $1.79. Get a scantool and monitor IAT temp. Dial it to +60C. Then go drive the car wot and monitor timing. You should be down quite a bit of timing. Lower the temp and at WOT you will see the timing increase.
NOTE : The timing table is not adjusted at idle so checking idle spark advance will not be helpful you will need to verify timing while at WOT.
NOTE 2 : You need to monitor KR and Timing at WOT. If you have knock, you will not be able to get more timing even if the knob is set to allow for more timing; however, yo ushould have more KR than you would with the knob with the timing adjusted downward....
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